Field of the Invention
This invention relates to RF controlled proximity fuzes for projectiles.
Description of the Related Art
A proximity fuze is a fuze that detonates an explosive device automatically when the distance to the target becomes smaller than a predetermined value. British Army researchers Sir Samuel Curran and W. A. S. Butement developed a proximity fuze in the early stages of World War II under the name “VT”, an acronym of “Variable Time fuze”. The system was a small, short range, Doppler radar. Proximity fuzes may be incorporated into a projectile, which includes self-propelled missiles, rockets and gun-launched munitions. Proximity fuzes are designed for targets such as planes, missiles, ships at sea and ground forces. They provide a more sophisticated trigger mechanism than the common contact fuze or timed fuze.
U.S. Pat. No. 3,113,305 entitled “Semi-Active Proximity Fuze” uses a remote source of electromagnetic radiation to illuminate a target. The missile includes a single antenna with rear and front lobes to receive radiation directly from the source and to receive reflections from the target. The missile uses an analog receiver to mix the signals to detect the amplitude of the Doppler beat frequency. A firing circuit detonates the missile when the amplitude peaks.
U.S. Pat. No. 3,152,547 entitled “Radio Proximity Fuze” uses a shell that contains a micro-transmitter that uses the shell body as an antenna and emits a continuous wave of roughly 180-220 MHz. As the shell approaches a reflecting object, an interference pattern is created. This pattern changes with shrinking distance: every half wavelength in distance (a half wavelength at this frequency is about 0.7 meters), the transmitter is in or out of resonance. This causes a small oscillation of the radiated power and consequently the oscillator supply current of about 200-800 Hz, the Doppler frequency. This signal is sent through a band pass filter, amplified, and triggers the detonation when it exceeds a given amplitude.